Mystery deaths???

HEY GUYS
hope someone can shed some light here.
i have a small 60cm tank in which i grow out my baby platies.
i have many many babies in here.
a couple of months ago i acquired some baby white clouds. they have been in this tank with the baby platies since i got them and everybody has been fine and well.
On Saturday my white clouds started dying off one by one... dying like flies.
i did a small water change on sat eve, and still continued losing them.
On sunday monrning i checked the PH and the nitrates.
The PH was low - 6 or below(test only shows till 6) and the nitrates were up a little. So i did a 50% waterchange, and stabilised the PH. PH tested fine thereafter and i have lost 1 more cloud since then.
I have only got 2 left now...
But my question is, howcome throughout this whole problem not one platy has died...?

How does that happen and what could have been the problem?

 

Very hard to diagnose from your description..... pH of 6, should've affected your Platies even more...... Did your White clouds just keel over & die or was there any prominent symptoms??.....

 

well sort of.
their fins would droop, they would stuggle to swim eventually.
they hung on top of the water between the floating plants, almost like they were hanging on... then die.
I lost like 30 clouds????
WEIRD:evil::evil::evil:

 

Was there any salt in the water? Don't platies need saline water like molies?

 

nope

not as far as i know

 

White clouds are pretty sensitive fish. If you shine light at an angle at the surface of the water and see oily swirls . . . this is your killer.

Sometimes we put our hands in the tank to move stuff and at the same time introduce oils (soap,lotion,moisturizer,food oil,perfume) into the water without knowing.

Since these fish roam the Mid to Surface range and platies mid to bottom range, the killer is not likely Ph or temperature but a case of chemical leeching.